A184 Non-Cirrhotic Hyperammonemia Secondary to Extrahepatic Portosystemic Venous Shunt Presenting as a Congnitive Dysfunction: A Case Report and Literature Review

Abstract

Background Hyperammonemia secondary to liver disease is a very common cause of hepatic encephalopathy (HE) and it is easily recognized in patients with advanced liver disease. Non-cirrhotic causes of hyperammonemia are rare, particularly extrahepatic portosystemic venous shunts (EPS). The majority of these shunts are between a mesenteric vein and the inferior vena cava. We report a case of a non-cirrhotic hyperammonemia secondary to a shunt between the superior mesenteric vein (SMV) and the right renal vein (RRV) that presented with encephalopathy. Diagnosis was delayed due to lack of awareness of non-cirrhotic hyperammonemia underscoring the importance of measuring ammonia in all patients presenting with encephalopathic symptoms irrespective of their liver function. Aims To report our experience with a patient with unexplained cognitive dysfunction that was eventually attributed to hyperammonemia secondary to a rare non-cirrhotic portosystemic shunt. Also, we discuss the differential diagnoses of non-cirrhotic hyperammonemia and the pathophysiology, classification and diagnosis of spontaneous portosystemic shunts. Methods A retrospective chart review Results A 57-year-old woman with longstanding essential tremors on topiramate presented with a 30-month history of recurrent disabling episodes of unexplained “zoning out”. Her neurologists undertook extensive investigations which excluded primary neurological conditions. These episodes persisted despite discontinuation of topiramate, treatment of urinary tract infection (UTI) and continuing daily prophylactic antibiotics for recurrent UTIs as presumed etiologies. Due to her unexplained and disabling symptoms she was referred to an internist. During further evaluation, ammonia level was measured for first time, in the absence of any obvious features of chronic liver disease, and the level was strikingly elevated 152uml/l. Hence, an abdominal CT was obtained and revealed a prominent shunt between SMV and RRV. The patient was diagnosed with non-cirrhotic hyperammonemia secondary to EPS. She is currently stable on lactulose and rifaximin with a drop in her ammonia level to 63uml/l, and an interventional radiological procedure is being considered. Conclusions While hyperammonemia is most commonly related to liver failure, our case highlights the importance of awareness of non-cirrhotic hyperammonemia. Any unexplained change in level of consciousness, cognition and/or behavior merits measurement of serum ammonia irrespective of clinical liver status. Funding Agencies None